It is likely that the next pope will be elected from among the 209 current cardinals. Being a cardinal is not required to be elected as pope, although tradition of centuries has favored cardinals in papal elections. The last non-cardinal to be elected was Pope Urban VI in 1378.
In fact, a pope does not have to be a bishop or even a priest before being elected. In fact, under canon law any baptized Catholic* man who is not a heretic, or in schism, or notorious for simony is technically eligible. Upon election, the newly elected man would receive baptism and Holy Orders as necessary. If not a bishop, he would be ordained as bishop by the Cardinal Dean immediately before becoming Supreme Pontiff.
In recent years, men who were elected pope have all been priests and bishops as well as being cardinals. 1455′s election of Pope Callistus III was the last time a non-priest was elected as pope. The most recent time a non-bishop was elected was in 1831 with the selection of Pope Gregory XVI. All 203 of the current cardinals are priests and bishops.
*for the question of whether a candidate needs to be Catholic, see “For Further Reference” below.